| The experiment was conducted to study the effects of steam-flaked corn (SFC) on the performance, metabolic parameters, excretion of nitrogen and phosphorus and the optimal dose of Holstein cows during early lactatation period.Eight primiparous healthly Holstein cows in early lactatation with similar milk yield and parturition date were selected in a replicated 4×4 Latin square design, and were assigned randomly into 4 groups each with 2 replicates. Steam-flaked corn contents in the experimental ration were dividedly 0%, 10%, 20% or 30% of the concentrate. There were four 28-d periods. The results indicated that dry matter intake (DMI) was unaffected by diet (P>0.05), but steam-flaked rather than dry- ground corn (DGC) in diets could significantly increase the feed efficiency (4%FCM/DMI) (P<0.05). The apparent digestibility of nutrients were unaffected by diet (P>0.05). The milk yields (SFC supplement at 10%, 20% or 30%, separately) were respectively higher 1.76 kg/d (P >0.05), 2.38 kg/d (P <0.05), 2.54 kg/d (P<0.05) than that of the control group, but no significant difference appeared among the treatment groups (P>0.05); FCM yield for cows fed concentrate diets containing 20% or 30% SFC was separately significantly increased 2.78 kg/d (P<0.01) or 2.87 kg/d (P<0.01) than the control diet. The percentages of milk fat, protein, lactose and non-fat solid (SNF) were unaffected by diet (P>0.05), but tended to increase except milk fat; The yield of milk fat, protein, lactose and non-fat solid were increased (P<0.05) for cows fed SFC diets. Milk fat and protein yield of the 30% group was significantly higher 0.11 kg/d (P<0.01) and 0.1 kg/d (P<0.01) than those of the control group (1.07 kg/d vs 0.86 kg/d). Steam-flaking corn tended to decrease SCC by 8.73% (P>0.05),11.92% (P>0.05),17.88% (P>0.05), respectively; SFC in diets could significantly increased serum glucose concentration (P<0.05) and decreased serum non-etherified fatty acid (NEFA) concentration (P<0.01). Compared to the control group, the serum glucose concentration were separately increased 3.92mg/dL (P>0.05), 6.25 mg/dL (P<0.05)and 6.96mg/dL (P<0.01),the NEFA concentration were separately decreased 23.92 mg/dL (P<0.01), 29.84 mg/dL (P<0.01), 38.93 mg/dL (P<0.01);SFC in diets could significantly decreased Blood urea nitrogen (BUN) and Milk urea nitrogen (MUN) concentration (P<0.01). Compared to the control group, the BUN concentration were separately decreased 1.11mg/dL (P>0.05), 4.19 mg/dL (P<0.01)and 4.81 mg/dL (P<0.01),the MUN concentration were separately decreased 1.70mg/dL (P<0.05), 2.48 mg/dL (P<0.01), 2.92 mg/dL (P<0.01);the serum calcium (Ca) and phosphorus (P) were tended to increased (P>0.05).Comparing with the control group (0%SFC), SFC diet had decreased the excretion of nitrogen and phosphorus, the excretion of nitrogen of the cows fed with the SFC diets were decreased by 4.23%(P>0.05),9.37%(P<0.05)and 10.29%(P<0.05),and the excretion of phosphorus were decreased by 1.93% (P>0.05),2.59% (P>0.05)and 5.19% (P>0.05).The income of feeding a cow with the diet Including SFC were separately increased 4.93 RMB/d, 6.31 RMB/d and 6.42 RMB/d ,comparing with the control group.In summary, The SFC in diet could improve the performance and economic profit of feeding, decrease the excretion of nitrogen and phosphorus. As all of qualification were concerned, the optimal dost of SFC was 10% to 20 % in the concentrate of dairy cows in early lactation.
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